1. Field of the Invention
The present invention relates to a method of manipulating semiconductor substrates or wafers.
2. Description of the Related Art
Electrostatic carrier systems have long been known in the art and are described in several patents. The prior art is outlined in the following overview articles which refer to the patent literature: Shermann et al.: Semiconductor International V Jul. 20, 1997, 319-321; Olsen et al.: Rev Sci. Instrum. 66 (2) February 1995, 1108-14; Watanabe et al.: Jpn. J. Appl. Phys. Vol (32) 1993, 864-71; Hartsough Solid State Technol., 97 (1) 1994, 91-98.
Consequently, it is known in the art to fix semiconductor substrates or wafers by means of electrostatic carrier devices in machines for treating wafers. However, the wafers are separated from the electrostatic carrier system after the end of each process step.
The transfer of wafers using electrostatic carrier systems from and to any type of substrate carrier has also already been described, for example, by Shermann et al. However, all these devices have in common that the wafer remains connected to the electrostatic carrier system only during a process or manipulating step within a processing machine.
Systems of this type meet all the requirements which are made of them, at least as far as the manipulation is concerned in wafers having standard thicknesses of about 200 μm up to thin wafers of about 100 μm. In the case of thicknesses of about 200 μm to about 100 μm, the requirements are only met if the wafer is additionally reinforced with a plastic film or tape attached or glued to it. Another difficulty is the fact that thin polished wavers are extremely sensitive to breakage, as long as defects caused by polishing are not removed by wet or dry stress relief etching.
In the case of wafers of having a thickness of below about 100 μm (the technical limit is presently at 20 μm), the prior art teaches that the wafers have been applied onto a rigid carrier by gluing (using wax, a double-sided plastic film or tape, pure adhesive) or even by soldering, in order to reduce the danger of breakage and the significant bending of the destressed wafers.
However, these methods are not satisfactory because, with the exception of soldering, the temperature stability of the connection is too low and because in all methods the separation of the thin wafers from the carrier is technically very complicated and problematic because of the danger of breakage. An exception in this connection is only the use of adhesives which almost completely lose their adhesive power after having been exposed to ultraviolet light. However, at the present time, these adhesives are not heat resistant at temperatures above about 80° C.